1. Field of the Invention
This invention relates to the preparation of stable solutions of the polymerization reaction product, poly(paraphenylene terephthalamide) acid crumb from which fibrous products can be directly prepared.
2. Description of the Related Art
In the manufacture of poly(paraphenylene terephthalamide) U.S. Pat. No. 4,308,374 issued Dec. 29, 1981 on the application of Vollbracht et al. requires isolating poly(paraphenylene terephthalamide) polymer from the acid crumb reaction product by thoroughly washing the acid crumb to separate the polymer from the organic solvent, the inorganic salts and the hydrogen chloride formed during the reaction. The isolated, washed, and dried poly(paraphenylene terephthalamide) polymer can then be dissolved for example, in accordance with the teachings of U.S. Pat. No. 3,869,429 issued Mar. 4, 1975 on the application of Blades, in concentrated sulfuric acid, to yield a dope from which fibrous products can be produced.
There now has been discovered, through the solvent combination of this invention, a process to prepare stable solutions directly, using poly(paraphenylene terephthalamide) acid crumb, and to make fibrids from these solutions. The solvent combination of this invention permits preparation of a solution of poly(paraphenylene terephthalamide) acid crumb by dissolving the poly(paraphenylene terephthalamide) acid crumb without the usual steps of isolating, washing and drying the polymer before dissolving the polymer to make the poly(paraphenylene terephthalamide) dope. Furthermore, the solvent combination of this invention eliminates the need for the solvents of the past, such as sulfuric acid, which degrade the polymer, corrode the system components and require costly safety precautions.
U.S. Pat. No. 4,785,038 issued Nov. 15, 1988 on the application of Sweeny addresses the problem of difficultly soluble pure polymers such as, for example, poly(metaphenylene isophthalamide), poly(parabenzamide), and poly(paraphenylene terephthalamide) and teaches a solvent system that obviates the need for such harsh solvents as concentrated sulfuric acid. Clear solutions of such polymers are obtained in a carefully defined mixture of a liquid sulfoxide, base, and alcohol or water. A typical solution from the process taught by Sweeny comprises approximately 88% dimethyl sulfoxide, 5% base, 3% pure polymer and 4% methanol. The process of Sweeny does not yield clear solutions of poly(paraphenylene terephthalamide) acid crumb reaction product at concentrations greater than 2% by weight poly(paraphenylene terephthalamide) which are needed for preparation of fibrids.